Unique Co-Catalytic Behavior of Protic Ionic Liquids as Multifunctional Electrolytes for Water Splitting

Graphical DEAFening : For the first time, a protic ionic liquid, diethylammonium format, is used as a multifunctional electrolyte in a water-splitting cell, demonstrating a unique role as co-catalyst. Hydrogen production from water splitting holds great promise for solving today's energy crisis but it is challenging to have high efficiency and low cost. For the first time, a protic ionic liquid (PIL), diethylammonium formate (DEAF) was used as a multifunctional electrolyte in water splitting, demonstrating a unique role of co-catalyst for the hydrogen evolution reaction (HER) with the highest current density (21 mA cm −2 at −0.5 V) and the most positive onset potential (−0.002 V) in comparison to aprotic ILs and commonly used inorganic salts. Moreover, the concentration of PIL and temperature of electrolyte solution were optimized. The possible mechanism for the multifunctionality and high performance for water splitting using this PIL was proposed using X-ray photoelectron spectroscopy (XPS). The high performance for HER, simplicity and low cost for synthesis, and unique properties make DEAF highly promising as an electrolyte toward water splitting.